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Two United Airlines flights were forced to return to Newark Airport after takeoff, in separate incidents within a 24-hour period.

A Berlin-bound United flight had to make an emergency landing Saturday evening because of an engine issue. A second United flight also had to return to the airport Sunday morning -- this time because of a smoke condition in the cockpit, authorities say.

United Flight 409, bound for Seattle, returned to Newark at 9:15 a.m. because of the smoke condition, which had dissipated by the time the plane landed, authorities said.

On Saturday, United Flight 96 was headed toward Germany when the Boeing 757 experienced a mechanical issue, according to an airline spokesman.

“When the plane took off, it was shaking so much,” said Yaser Haj. “We [smelled] it. We saw fire from the back.”

A woman who lives near the airport told the paper she first heard loud noises coming from the plane.

"We heard, Bang! Bang! Bang!" Suzanne Finelli said. "Every time there was a bang there were flames coming out. The plane looked so low, I thought it was going to fall out of the sky."

Flight 96 eventually returned to Newark and landed safely. It had taken off at about 5:50 p.m. and was back at the airport by about 8:10 p.m.

On Sunday, the Federal Aviation Administration said one of the engines on Flight 96 apparently overheated during takeoff. An agency spokeswoman said that contrary to published reports, the aircraft didn't blow a tire during takeoff.

There were 173 passengers and crew members on board Flight 96. Passengers were able to fly out to Berlin on another flight early Sunday.

In a statement United said that Flight 409 to Seattle "experienced an unusual smell in the cockpit, and out of an abundance of caution, returned to Newark, landing safely."

The airline said they were "working to re-accommodate customers to their final destinations."

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